1. Field of the Invention
The present invention relates to a broadcasting receiver and a channel searching method in the broadcasting receiver, and more particularly, to a broadcasting receiver having two digital receiving units and a channel searching method in the broadcasting receiver having the two digital receiving units.
2. Description of the Prior Art
In recent years, ground wave digital television broadcasting has been developed. The transition from current analog broadcasting to digital broadcasting is being made. In a period of the transition, it has been expected that a channel map is frequently changed by newly opening a digital broadcasting station and changing frequencies, for example. Therefore, a receiver is required to make an efficient channel search.
On the other hand, smooth channel selection can be carried out by previously recognizing on which channel (frequency) broadcasting is being performed in the case of receiving, that is, on which channel broadcasting is receivable. Channels on which broadcasting is being performed differ for each area. Therefore, a channel map is produced by making a search over all broadcasting channels to determine on which channel broadcasting is being performed when a receiver is installed.
The channel search is made by tuning in to channels in a predetermined order with respect to a tuner and judging whether or not broadcasting is being performed on the channel based on whether or not a normal signal to be received can be obtained from the tuner.
Description is now made of an example of the channel searching operation of the receiver using FIG. 1.
FIG. 1 illustrates the configuration of a broadcasting receiver.
The broadcasting receiver comprises two groups of digital receiving units for receiving ground wave digital broadcasting. One of the digital receiving units comprises a first digital tuner 101, a first digital demodulator 102, and a first TS decoder 103. The other digital receiving unit comprises a second digital tuner 201, a second digital demodulator 202, and a second TS decoder 203.
A microcomputer 300 receives, through a remote control signal receiver 301 for receiving an operation signal transmitted by radio from a remote control 401 or a main body operation key 302, the operation signal. The microcomputer 300 starts a channel searching operation by receiving an operation signal representing a channel search command.
The channel search has been conventionally made using the one digital receiving unit. That is, the microcomputer 300 outputs to the first digital tuner 101 a channel selection instruction for tuning in to a channel having the lowest frequency on which broadcasting may be performed when it receives the operation signal representing the channel search command. Out of signals inputted to the digital tuner 101 from the ground wave broadcasting antenna 100, the signal selected by the digital tuner 101 is inputted to the first digital demodulator 102, and is subjected to demodulation processing conforming to a modulation system. Generally, a digital TV broadcasting signal is subjected to OFDM (Orthogonal Frequency Demodulation Multiplexing) modulation, for example, and is subjected to OFDM demodulation by the first digital demodulator 102.
If a normal signal is broadcast, it is outputted as an MPEG (Motion Picture Expert Group) transport stream after being previously subjected to processing for error correction. The demodulated MPEG transport stream is subjected to decoding processing by the first TS decoder 103, and is outputted as elementary streams such as a video, an audio, etc., so that a video signal and an audio signal are restored by a video/audio decoder 104.
The microcomputer 300 judges whether or not a normal digital signal is received on the channel which the digital tuner 101 is instructed to tune in to on the basis of the state of the first digital demodulator 102. Specifically, it is judged whether or not the normal digital signal is broadcast depending on whether or not the first digital demodulator 102 can establish synchronization of the received digital signal. However, a method of judging whether or not the normal digital signal is received is not necessarily limited to the same.
Information such as a broadcasting station name sent from a broadcasting station is acquired on the basis of data obtained by the first TS decoder 103. The presence or absence of broadcasting may be judged depending on whether or not the broadcasting station name can be specified. When it is judged that the normal digital signal is received, the microcomputer 300 stores in a memory 303 information for channel selection (receivable channel information) such as a frequency, a broadcasting station name, and a channel number.
The microcomputer 300 then outputs an instruction to tune in to a channel on the high frequency side adjacent to the current channel, for example. The microcomputer 300 judges whether or not the normal digital signal is received on the channel tuned in to in the same manner as described above, and stores in the memory 303 information for channel selection (receivable channel information) such as a frequency, a broadcasting station name, and a channel number when it is judged that the normal digital signal is received. Such an operation is repeated over all channels, to store in the memory 303 receivable channel information indicating on which channel broadcasting is being performed.
At the time of a normal operation, the microcomputer 300 receives a channel selection instruction from a user through the remote control signal receiver 301 or the main body operation key 302, and refers to data in the memory 303, thereby outputting to the first digital tuner 101 a channel selection instruction corresponding to the channel desired by the user.
As described in the foregoing, in the channel search for digital broadcasting, it is judged whether or not a normal signal can be received, and it is necessary to confirm the contents of digital data in order to extract a broadcasting station name or the like. Therefore, it generally takes much time to judge whether or not broadcasting is being performed on the channel.
Furthermore, in Japanese ground wave digital broadcasting, there are a plurality of types of broadcasting modes, and all combinations of the modes must be tried. Therefore, it takes more time to make the judgment. Thus, the channel search for digital broadcasting requires more time than the channel search for conventional analog broadcasting. When a channel search must be frequently made as in a period of transition to digital broadcasting, a viewer is forced to feel inconvenience.
An example of a VTR-integrated receiver is one comprising two groups of digital receiving units, as shown in FIG. 1. In such a receiver, it is considered that a channel search is made using the two digital receiving units. That is, channels to be searched for are previously divided into two groups, to search for each of the channels in the one group using the one digital receiving unit, while searching for each of the channels in the other group using the other digital receiving unit.
When a channel search is made by such a method, a processing time period can be made shorter, as compared with that in a case where a channel search is made using only one digital receiving unit. Even in the search for one channel, however, a search time period differs depending on whether or not there is broadcasting. When the number of channels handled by each of the digital receiving units is fixedly assigned, as described above, it takes longer to make the channel search using the one digital receiving unit than the channel search using the other digital receiving unit.